I am personally skeptical of speculation that this is a sign that Roberts is shifting. However, I am somewhat more compelled by Richard Posner’s argument that the reaction to his opinion by the Court’s most conservative justices, Republican members of Congress, and the right-wing media may itself lead Roberts to rethink his ingroup allegiances:

Because if you put [yourself] in his position … what’s he supposed to think? That he finds his allies to be a bunch of crackpots? Does that help the conservative movement? I mean, what would you do if you were Roberts? All the sudden you find out that the people you thought were your friends have turned against you, they despise you, they mistreat you, they leak to the press. What do you do? Do you become more conservative? Or do you say, ‘What am I doing with this crowd of lunatics?’ Right? Maybe you have to re-examine your position.

In an interesting interview with NPR, Posner explains how he himself has been influenced politically by a negative reaction to what he characterizes as a growing “goof[iness]” of the Republican Party. Listen to the interview here.